An IP code states what an enclosure protects its contents against. For extension cords and power distribution units it decides whether the equipment belongs outdoors, on a construction site, or strictly in a dry room. The two digits after the letters IP carry two independent pieces of information.

First digit: solids and dust

• 2 – protection against objects larger than 12.5 mm, that is, against contact with a finger.
• 4 – protection against objects from 1 mm upwards, such as wire or screws.
• 5 – dust protected to a degree that does not interfere with operation.
• 6 – fully dust tight.

Second digit: water

• 0 – no protection at all.
• 4 – protection against splashing water from any direction.
• 5 – protection against water jets from a nozzle.
• 7 – protection against short periods of immersion.

What this means in practice

• IP20 – dry interiors only. The typical office socket strip. Not suitable for a balcony or a damp garage.
• IP44 – the minimum for outdoor work. It handles rain and splashes, but not flooding and not lying in a puddle.
• IP54 – dust protection on top of that. The natural choice for construction sites, workshops and renovation work.
• IP67 – dust tight and able to survive brief immersion. For situations where the equipment may end up in water or mud.

The most common mistake when choosing

An IP rating applies to the enclosure when it is closed. A socket with a hinged lid meets its stated rating only with the lid down — and, with a plug inserted, only if that plug is seated and secured correctly. An open IP44 socket lying on wet ground offers no protection whatsoever, however accurate the product marking may be.

The second trap is confusing IP with mechanical strength. A high IP number does not mean the enclosure will survive being driven over or struck. That is covered by a separate figure — the IK code.